Human herpesvirus (HHV) causes serious illnesses such as cancer and genital herpes. The HHV family of viruses expresses proteases that are required for viral maturation and capsid formation and, therefore, infectivity. These serine proteases are unique among other known serine proteases in that they are active only in a dimeric form. Protein-protein interactions represent a validated and attractive therapeutic strategy, and methods for designing drug-like molecules that act to prevent such interactions have increased and improved over the past decade or more. In this project, the overarching aims are to fully understand and improve upon small molecules that have been characterized as protein-protein interaction inhibitors active against numerous HHV family members. In aim one, the project proposes to employ X-ray crystallography in order to fully understand the similarities and differences in binding modes of small molecule allosteric inhibitors against two different herpesvirus family members, Kaposis' Sarcoma-associated Herpesvirus (KSHV) and cytomegalovirus (CMV). X-ray crystallography is a state-of-the-art technique that can provide invaluable information at the atomic level and can guide drug design, and will be employed in aim one. In aim two, small molecule fragments that have been identified as potential dimer disruptor compounds will be probed with nuclear magnetic resonance techniques that can identify potential regions of dissimilar fragments that can be linked together. These linked fragments can improve the dug-likeness of the small molecules. Finally, in aim three, the project aims to validate the therapeutic potential of the strategy by comparing the efficacy of novel, improved compounds to that of one of the standards of care, ganciclovir. Overall, this project could provide compounds that are drug-like in nature, provide proof of concept for a novel therapeutic rationale, and could lead to the treatment of herpesvirus infections that cause serious illness.